It is known that thin flexible endoscopes with a diameter less than 2.5 mm are susceptible to damage due their delicate structure. After repeated use, image guides or light guides may break, as a result of which the flexible endoscope becomes useless. In such flexible endoscopes there must be arranged light guides for adequate illumination of the area of examination and surgery and image guides with sufficient picture elements, within a very small diameter. These are necessary in order to facilitate manipulations with accessory instruments in an area of treatment such as for example on body tissues, without endangering the patient. At least one channel for accessory instruments or for the supply and removal of fluids must also be provided. The endoscope must also enable the user to guide the distal end of the flexible shaft through body cavities or ducts e.g. blood vessels or ureters to the treatment area. This is customarily achieved by an operating wire leading to the distal end of the flexible shaft.
If, in conventional flexible endoscopes, for example a light guide or image guide is broken, then extensive repair is necessary. Sometimes this cannot even be carried out at all on account of the design of the endoscope. Therefore there has been a tendency to divide such endoscopes into individual sub-assemblies which can be replaced by sub assemblies when damage occurs.
Instruments in which the handle and the eyepiece are not designed as a structural unit, but as sub-assemblies which can be fixed together, are known. An example of this can be found in WO85/02101 which concerns a non-controllable catheter.
With flexible endoscopes it is normal to design the flexible shaft with its proximal connecting portion as a unit which can be fixed releasably to a handle rigidly connected to an eyepiece. An example of an embodiment of such an arrangement is shown in U.S. Pat. No. 4,911,148. In this endoscope one sub-assembly is formed by a flexible shaft provided with a light guide, an image guide, an instrument channel and an operating wire with a connecting portion. The second sub-assembly comprises a handle with a focusable eyepiece fixed thereto. The image guide extends beyond the proximal end of the first sub assembly and is surrounded by a sleeve which corresponds to a second sleeve in the handle portion when the endoscope is assembled. This ensnares centring of the two sub-assemblies. Very elaborate mechanics for adjustment of the operating wire are provided which means that manufacture is expensive. If for example there is damage to the eyepiece portion, then the fact that the instrument consists of only two sub-assemblies means that the whole handle/eyepiece sub-assembly must be exchanged and repaired, or even thrown away, as the eyepiece portion cannot be removed as an individual component. Furthermore control of the endoscope shaft is by turning an adjusting ring, so that handling of the instrument is not easy for the operator.